This invention relates to microstrip antennas for an array antenna.
The transmitter side of a conventional antenna system such as described in "Present Solid State Phased Array Radars," Nikkei Electronics, July 17, 1972, is shown in FIG. 14. This antenna system includes a microstrip antenna 1 which is an elementary antenna, a high-power amplifier 2, a coaxial cable 3 connecting the microstrip antenna 1 and the high-power amplifier 2, a pin-diode phase shifter 4, and an oscillator 5. An example of the microstrip antenna 1 is shown in FIG. 3.75 on page 110 of "Antenna Engineering Handbook," Ohm Co.
FIGS. 15(a) and 15(b) show a conventional microstrip antenna. The microstrip antenna 1 includes a radiation conductor 6 with the center 10, a ground conductor 7, a dielectric body 8 sandwiched between the radiation and ground conductors, a feeder 11 connected to the radiation conductor 6 at a feeding point 9, and a plated through-hole 12 connecting the radiation conductor 6 and the ground conductor 7.
In operation, a signal generated by the oscillator 5 is provided with a shift quantity quantized by the pin-diode phase shifter 4. The signal is then amplified by the high-power amplifier 2 to excite the microstrip antenna 1 via the feeder 11. When the power is supplied to the radiation conductor 6 at the feeding point 9 via the feeder 6, the electromagnetic field within the dielectric body 8 between the radiation conductor 6 and the ground conductor 7 resonates in such a way that it has an peak value at the periphery of the radiation conductor 6, transmitting an electromagnetic wave into space.
The diameter of such a microstrip antenna excited in the TM11 mode is about 0.586/.epsilon.r wavelength, wherein .epsilon.r is the relative permittivity. Consequently, the degree of mutual coupling in an array antenna is disadvantageously large. In addition, there is no room for providing an impedance matching circuit if necessary. As a result, in addition to the increased system size, the loss due to the feeder between the amplifier and the element antenna is disadvantageously high.